An image forming apparatus such as an electrophotographic copier, printer, or facsimile apparatus is equipped with a fixing apparatus that heat-fixes an unfixed toner image formed on the surface of a recording material. There is a fixing apparatus wherein a pressure nip is formed between a fixing roller and a heating roller pressing against that fixing roller, recording material bearing toner is gripped and transported to this pressure nip, and an unfixed image is heated from the fixing roller side and is heat-fixed onto the recording material surface.
A variety of methods have been developed as fixing roller heating methods. For example, a method is known whereby a fixing roller is composed of a film guide comprising an insulative cylindrical member that does not prevent the passage of magnetic flux and electromagnetic-induction heat-producing film (fixing film) wrapped around the outer periphery of this film guide, a magnetic field generated by a field generation section comprising an exciting coil and core provided outside the pressure nip area is applied and induction heating performed, and as the fixing roller rotates, the heated area moves to the pressure nip and heat-fixes the toner. Alternatively, a method is known whereby a fixing belt of electromagnetic-induction heat-producing film is suspended between a fixing roller and heating roller, the fixing belt is induction-heated by the application of a magnetic field to the fixing belt sliding over the heating roller by a field generation section provided opposite the heating roller, and the heated fixing belt moves to the pressure nip and heat-fixes the toner.
In both methods, a control circuit (microcomputer) generally performs temperature control in order to maintain the temperature of the rotating heating member (fixing film or fixing belt) at a temperature suitable for fixing. The control circuit not only controls the rotating heating member at the optimal temperature, but can also be given a control function of preventing the problem of erroneous heating when rotation of the rotating heating member stops. Specifically, a rotation detection section (optical sensor) is provided that detects rotation of the fixing film, and when rotation of the fixing film stops or falls to a predetermined speed or below, the control circuit (microcomputer) stops or suppresses the power supply to the exciting coil, and suppresses heat output (see Patent Document 1, for example).    Patent Document 1: Unexamined Japanese Patent Publication No. 2001-203072